More Durable Concrete: The Need & The Rationale

 

Concrete is the most widely used material of construction, with a consumption rate of 22 billion tons/yr. Production of concrete accounts for more than 4 billion tons/yr CO₂ emissions and 20 billion GJ/yr energy use, most of which is associated with the manufacturing of cement. The concrete-based infrastructure supports diverse economic and social activities. The sustained growth in cement consumption over several decades reflects upon the buildup of an immense concrete-based infrastructure. Aging of this infrastructure has mounting economic and safety implications. 

While concrete occupies a significant volume of vast infrastructure systems, the expenditures on concrete materials constitute a relatively small fraction of the total infrastructure costs. Deterioration of concrete and corrosion of reinforcing steel under weathering, thermo-mechanical and chemical effects are key factors governing the maintenance and repair requirements and service life of the concrete-based infrastructure. More durable concrete materials would thus yield improportionally large life-cycle benefits. The improved service life of the concrete-based infrastructure would also translate into reduced CO₂ emission and energy use, which would be magnified if Portland cement is replaced with a cementitious binder of reduced carbon footprint and energy content.

Deterioration of concrete and corrosion of the reinforcing steel are complex phenomena. Concrete is prone to microcracking at young age, primarily due to the internal and external restraint of shrinkage movements. The pore structure of concrete together with these microcracks facilitate transport of moisture, aggressive solutions and gases into concrete. These transport phenomena facilitate various mechanisms of concrete deterioration, including freeze-thaw damage, alkali-aggregate reaction, sulfate attack, carbonation, acid attack, and corrosion of the reinforcing steel. These deterioration mechanisms together with the growth of microcracks and cracks under mechanical (including fatigue) loading and restrained dimensional movements compromise the barrier qualities and accelerate the degradation of concrete. Abrasion, erosion and cavitation are also among the mechanisms of concrete degradation in such concrete-based infrastructure systems as pavements and hydraulic structures.

Needs Related to Antimicrobial Surfaces

 

Surfaces in the building interiors can serve as reservoirs for pathogenic viruses and bacteria. As a result, infectious diseases are commonly transmitted through surfaces on which aerosols (ejected orally or nasally by already infected individuals) have settled. Antimicrobial surfaces can play key roles in preventing the spread of diseases via contaminated building surfaces.

Building occupants establish frequent contacts with such surfaces as (door, faucet, cabinet and toilet flush) handles, countertops, floorings, walls, and light switches. Technologies have been developed, but not broadly adopted in building applications, to make surfaces inherently antiviral and antibacterial. The cost burden of many such technologies have prohibited their broad building applications. There is a need for lower-cost methods of rendering building surfaces antimicrobial in both production and remedial settings.

Various test methods are available to assess the antimicrobial qualities of surfaces. These tests, however, cannot evaluate the long-term stability of antimicrobial surfaces in different service environments. Most interior building products remain in service for decades. There is a need for accelerated aging procedures for evaluating the long-term stability of antiviral and antibacterial surfaces. Such test methods can help with identifying economically viable means of providing interior building surfaces with sustained antimicrobial attributes. The resulting health benefits can then be weighed against the corresponding costs in an effort to persuade owners, occupants, builders and product manufacturers to employ antimicrobial surfaces. Development of building codes requiring antimicrobial surfaces would tie into these efforts towards high-impact implementation of the technology.